I used fluent to model flow around NACA 0015.
I got cl & Cd for the same flow and airfoil from Xfoil and want to compare Xfoil results with fluent results.
I want to find Cl and Cd by fluent and my problem is the numbers which I have to enter for X,Y,Z of force vector.
do you know what should I put in there and how many iterations should I have at least to get acceptable answer for Cl and Cd?
Thank you in advance

enter 1 0 0 for Force Projection on x-axis
enter 0 1 0 for Force Projection on y-axis
enter 0 0 1 for Force Projection on z-axis
Now choose the right force you want to observe, and enable the plot option in monitor/force
Fluent will plot the accorded Coeff while iterating.
Your solution will be full converged if the the plotted coefficient remains constant while iterating.
You also have to set the right reference values for getting the right Coefficient

enter 1 0 0 for Force Projection on x-axis
enter 0 1 0 for Force Projection on y-axis
enter 0 0 1 for Force Projection on z-axis
Now choose the right force you want to observe, and enable the plot option in monitor/force
Fluent will plot the accorded Coeff while iterating.
Your solution will be full converged if the the plotted coefficient remains constant while iterating.
You also have to set the right reference values for getting the right Coefficient

when you do that it shows the values for the coefficient of pressure, so how do you work out CLift ??

enter 1 0 0 for Force Projection on x-axis
enter 0 1 0 for Force Projection on y-axis
enter 0 0 1 for Force Projection on z-axis
Now choose the right force you want to observe, and enable the plot option in monitor/force
Fluent will plot the accorded Coeff while iterating.
Your solution will be full converged if the the plotted coefficient remains constant while iterating.
You also have to set the right reference values for getting the right Coefficient

Hi max, one question..I am modelling a 2D airfoil, the right references values should be:

Area: What value should i use?? The edge length of the airfoil multiply by the depth???

Check tutorial 3: Modelling external compressible Flow.
The references values you give are independant from your solution.
Compute your model, and then you can apply your refences values.
Even if you gave wrong Ref. Values, you can correct them without re-iterating.
They are just factors.
Important are pressure and viscous forces computed during iterations

I have the same problem and your answer indeed helped me a lot. I have monitored the Cl and Cd and while iterating I found out that my coefficients are not constant in the plot what I am supposed to do in this situation. Please explain in details I am a beginner.

Hi max...i figure it out that if i change the depth on reference values i get differents cl y cd results..why is that if the equation is: Cl=F/(0.5*density*velocity*velocity*Area)..

Another question what if the angle of attack is different than zero, which velocity value on farfield should be taken to calculate the lift coefficient???

*Check Online Help >>> "For 2D problems, an additional quantity, Depth, can also be defined. "

*I would say you can take the cosine of your angle as factor. But since the angles are small, it won't affect your coeff (needs to be confirmed/invalidate from aero experts).
Check tutorial 3 and compare velocity value given in Ref. with Mach Number

you need also to check your residuals (plot/residuals...)
If all the residuals fall down, let iterate and check if your monitoring still stay constant.
Regarding your comparison between first and second order: write your force monitoring on a file (one file for 1st order, and one for second).
Write also case and data before switching to second order.

you need also to check your residuals (plot/residuals...)
If all the residuals fall down, let iterate and check if your monitoring still stay constant.
Regarding your comparison between first and second order: write your force monitoring on a file (one file for 1st order, and one for second).
Write also case and data before switching to second order.

What is GIS?

- What do you mean by all residuals fall down, I know how to get the residuals plt but how to know if they are down?

You have to have different mesh faces: example 10.000-20.000-30.000 and fix a parameter you want to study like Cf, Cl, Cd if any this values change less than 5% from mesh 10.000 and 30.000 means that it won´t be any different if you do a mesh with 40.000 faces because you are going to get very similar results, so you considerer that the 30.000 faces is okay for what you are doing.

read case & data from previous 1st order solution>> switch to 2nd order >> Initialize or don't(if you start from converged 1st order solution you will get faster convergence) >> compute and write your coeff in a different file.
Load your 2 graphs in excel, or whatever... and compare

- You don't need to generate a very fine grid: follow what RGRUIZ said

You have to have different mesh faces: example 10.000-20.000-30.000 and fix a parameter you want to study like Cf, Cl, Cd if any this values change less than 5% from mesh 10.000 and 30.000 means that it won´t be any different if you do a mesh with 40.000 faces because you are going to get very similar results, so you considerer that the 30.000 faces is okay for what you are doing.

hope it help you

Sorry but when you say different mesh faces do you mean the Sizing (maximum face size) I am using (car.x_t) geomtry file from Ansys.
and in the max face size by default its 1.78m.
can someone tell me the full steps of how to change mesh faces 10.000-20.000-30.000.

read case & data from previous 1st order solution>> switch to 2nd order >> Initialize or don't(if you start from converged 1st order solution you will get faster convergence) >> compute and write your coeff in a different file.
Load your 2 graphs in excel, or whatever... and compare

- You don't need to generate a very fine grid: follow what RGRUIZ said